Mount Everest, of course, is the world's highest point—if you don't count Mauna Kea or Ecuador's Mount Chimborazo (details here). But Everest hasn't always been the planetary champ. The Himalayas started to form "only" forty million years ago, a relatively brief time span in geologic terms. If you had a time machine, where would you find the planet's highest point ever? The answer might be closer to home than you realize.

New Jersey and Florida were once part of Africa.

Three hundred and thirty million years ago, the continent we now know as Africa pushed itself right into the eastern coast of North America, forming the supercontinent of Pangaea. During the Pangaean era, you could walk straight from New York to Morocco, and from Florida to Sierra Leone. In the year 300,000,000 BS (Before Snooki), the Jersey shore wasn't shore at all.

When continents collide, mountains pile up.

That continental smash-up is called the Alleghanian orogeny. Just like the collision of India with Asia that produced the Himalayas, the meeting of North America and Africa thickened the earth's crust there and pushed it upward into a giant plateau, with big rugged "fold mountains," like the wrinkles you might get by pushing two pieces of cardboard together, lining its eastward edge. The new Central Pangean Mountains lasted for a hundred million years until Pangaea started to break up, and today, their eroded remains are found in the Appalachians, the Scottish Highlands, and the Anti-Atlas Mountains of Morocco.

How to map mountains that don't exist anymore.

Paleoelevation—the measuring of ancient mountains—isn't an exact science, but from clues in the rock (levels of sediment, size of wrinkly synclines and anticlines, fossils, oxygen isotopes in minerals) it's possible to guess at the altitude of mountains that aren't there anymore. Today, the soil of the Appalachian Basin and the sand of the Outer Banks is full of the sediment produced as the Central Pangaean Mountains eroded away. Estimating that volume, geologists believe that the lowly Appalachians were once as high as the rugged Himalayas, and some now-vanished mountain in modern-day New Hampshire or North Carolina could easily have been taller than Everest is today.

In today's eroded Appalachia, it's a different story.

Time has taken its toll on the Appalachians. The range's highest peak, Mount Mitchell, is now about three thousand feet lower than Tibet's lowest point. How tall were the pre-Appalachians of Pangaea, though? Well, mountains are limited in their theoretical height by several processes. First is isostasy: the bigger a mountain gets, the more it weighs down its tectonic plate, so it sinks lower. The second is called the "glacial buzzsaw": the taller and colder a peak, the faster snow and ice will wear it away. Bottom line: mountains can get taller than Mount Everest in earth gravity, like the Appalachians probably did—but not much taller. Then they "peak."

Explore the world's oddities every week with Ken Jennings, and check out his book Maphead for more geography trivia.